Curing of unsaturated polyester resins



United States Patent" Ofilice 3,377,407 Patented Apr. 9, 1963 3,377,407CURING F UNSATURATED POLYESTER RESINS Donald M. Kressin, Getzville,Solomon C. Westbrook, Jr., Buffalo, Orville L. Mageli, Kenmore, andJames R. Kolczynslki, Williamsville, N.Y., assignors to Wallace &Tiernan, Inc., East Orange, N.J., a corporation of New Jersey NoDrawing. Continuation-impart of application Ser. No. 415,799, Dec. 3,1964. This application Apr. 17, 1967, Ser. No. 632,151

15 Claims. (Cl. 260-863) ABSTRACT OF THE DISCLOSURE Unsaturatedpolyester resins are cured using 3,5-dimethyl 3,5 dihydroxy 1,2peroxycyclopentane as the curing agent. Preferably a metal activator isalso present and the agent is added as a solution in an organic solvent.

CROSS-REFERENCE TO A RELATED APPLICATION This application is acontinuation-in-part of our copending application Ser. No. 415,799 filedDec. 3, 1964, now abandoned, and is filed pursuant to a requirement forrestriction.

This invention relates to peroxide curing of unsaturated polyesterresins and to novel peroxide formulations suitable for such use.

Methyl ethyl ketone peroxide solutions have been available in the UnitedStates since 1949, and have become standard catalysts for curing ofunsaturated polyester resins. To give room temperature cures they areused in combination with a cobalt or cobalt-amine activator system.

Because of the nature of the reaction between hydrogen peroxide andmethyl ethyl ketone, all commercial solutions contain from 3 to 5 ormore peroxidic components. These peroxides vary in catalytic activityand hazard. They are all too hazardous to be used in the pure state andtherefore the products are marketed in solution, usually in dimethylphthalate. Although peroxide manufacturers have improved the safetycharacteristics of some methyl ethyl ketone peroxide formulations,several products are of such a nature that careful handling isessential.

Several of the peroxidic components of a methyl ethyl ketone peroxidesolution are labile, that is, they can rearrange to form otherstructures without loss of active oxygen. This lends to changes inactivity of the mixture, since the components vary in reactivity towardthe acti vator systems. So called activity drift occurs which makes itdifiicult for the manufacturer to control production.

It has been discovered that unsaturated polyester resins may beconveniently cured at moderate temperatures by admixing 3,5 dimethyl 3,5dihydroxy 1,2 peroxycyclopentane therewith in a curing amount andmaintaining the admixture at the curing temperature for curing time; itis desirable to have present in the admixture an ethylenicallyunsaturated allyl phthalate.

The peroxide formulations consist essentially of 3,5- dime-thyl 3,5dihydroxy 1,2 peroxycyclopentane and organic liquid which has asubstantial solubility in water. Particularly suitable organic liquidsare alkanols, glycols, ethers, ketones, esters, heterocyclic amides,and/or heterocyclic alcohols; water containing solutions of theseorganic liquids are also especially suitable. Desirably the activeoxygen content of these formulations is between about 1 and 6 percent.

co-reactant such as a styrene or A particularly advantageous aspect ofthe invention lies in an admixture consisting essentially of anunsaturated polyester resin admixed with a curing amount ofperoxycyclopentane; this admixture may include an ethylenicallyunsaturated co-reactant such as a styrene or allyl phthalate.

Suitable curing formulations may consist of solid 3,5-dimethyl-3,5-dihydroxy-1,2-peroxycyclopentane intimately dispersed in aliquid so as to produce a paste composition; phthalate esters areparticularly suitable paste forming organic liquids. p

The peroxide utilized in the curing method and formulations of theinvention is prepared by the reaction of acetyl-acetone with hydrogenperoxide in an equi-molar ratio to form a cyclic peroxide named,3,5-dimethyl-3,5- dihydroxy-1,2-peroxycyclopentane.

This compound is believed to have the configuration: I. OH OH Proceduresfor the preparation of this peroxide which is hereinafter referred to asperoxide I are set forth in a paper of Milas et al. JACS 85, 222 (1963)and US. Patent No. 3,149,126, Sept. 15, 1964. Peroxide I herein named isshown in configuration in these publications as peroxide IV.

It has been discovered that peroxide I is extremely effective as acuring agent for the unsaturated polyester resins commonly cured withmethyl ethyl ketone peroxide known today (hereinafter methyl ethylketone peroxides will be referred to as MEK peroxides). The hereinafterset forth data will establish that amounts of peroxide I correspondingto a formulation having 4% active oxygen content are more effective ascuring agents than equal amounts of MEK peroxides in formulations having11% active oxygen content.

Peroxide I is effective in curing not only the unsaturated polyesterresin itself but also admixtures of these resins with co-reactants,especially the ethylenically unsaturated co-reactants such as members ofthe styrene hydrocarbons and allyl phthalate group of esters.

The effectiveness of peroxide I is favorably influenced, like the MEKperoxides, by the presence of a metal activator in the curing mixture.Any of the commonly used and known metal activators used for thisprocess may be used with peroxide 1. In general, the preferred metalactivators are compounds of cobalt, nickel, iron, manganese, 1 titaniumand vanadium. It is preferred to utilize oil soluble compounds,especially the cobalt compounds like cobalt naphthenate.

It is common to doubly promote MEK peroxides by the presence of an aminealong with the metal activator. Such double promotion may be used withperoxide I. However, peroxide I is so effective that double promotion isnecessary only in rare situation where extreme rate of cure isnecessary.

The effectiveness of peroxide I at moderate temperatures and itsresponse to promotion by metal activators permit a unique control ofcatalytic activity. It is possible to closely control curing times for aparticular resin at a particular temperature by varying either theamount of peroxide I added, or theamount of metal activator added.

By utilizing both peroxide I and a metal activator it is possible tocure-unsaturated polyester resins alone or in combination with aco-reactant such as styrene or diallyl phthalate at,- in effect roomtemperatures, of about -100 F. (about 15.5-37.8 C.). It is self-evidentthat the curing time will be dependent upon the type of unsaturatedpolyester resin, the type of co-reactant, if any, and the amountthereof, the amount of peroxide I 3 added, the type and amount of metalactivator, if any, added, as well as the curing temperature.

Peroxide I is a white crystalline solid. The curing can be carried out.by admixing the solid peroxide I into the resin to be cured. However,it is preferred to utilize either a liquid formulation or a pasteformulation'to introduce the peroxide I into the resin to be cured.

The liquid formulations may have the viscosity inherent to thecombination of constituents or the viscosity may be increased by theaddition of thickening agents.

It has been discovered that peroxide I may be converted to a liquidformulation by solution in organic liquids which have substantialsolubility in water (peroxide I is Very soluble in water itself). In thepreparation of peroxide I the water produced may be removed completelybut it is preferred to maintain some or all of the water in theformulation. In general, the liquid formulations of the inventionconsist essentially of peroxide I, organic liquid having substantialsolubility in water, and water. Although the active oxygen content ofthe formulation can vary widely, in general the formulations are made upto have an active oxygen content of between about I and 6 percent, e.g.,4%.

In general, the preferred organic liquid solvents which have substantialsolubility in water fall in the class of alkanols, glycols includingether 'glycols, ethers, ketones, esters, heterocyclic amides, andheterocyclic alcohols. Mixtures of these solvents may be used. Also,water containing solutions of these solvents may be used.

It has been observed that the presence of heterocyclic amides as aconstituent in these liquid formulations has advantages. It is preferredto utilize the N-alkyl 2-pyrrolidone where the alkyl has 14 carbonatoms. An especially preferred heterocyclic amide isN-methyl-Z-pyrrolidone, hereinafter referred to as NMZP.

The phosphate esters are particularly suitable because they impartburning resistance to the formulation. Triethyl phosphate is a preferredmember of this group.

Other particularly desirable species of solvents are propylene glycolsand tetrahydrofurfuryl alcohol.

In general, the more desirable liquid formulations include about 10-50%of peroxide 1; water from none to about 35%; and defined organic liquidabout 15-90%. When speaking of formulations all percentages are byweight and based on the total formulation. In the more preferredformulations the water content is not more than about 15%. More commonlythe peroxide I content falls in the range of about 20-40%.

As has been mentioned earlier, the presence of heterocyclic amide in theformulation is advantageous, and it is preferred that the formulationinclude at least about 3% of N-alkyl-Z-pyrrolidone where the alkyl grouphas 1-4 carbon atoms, and more preferably NMZP.

For purposes of illustration a number of especially preferredformulations are given.

(1) Peroxide I about 30; water about 12%; NMZP about 29%; and triethylphosphate about 29%.

(2) Peroxide I about 30%; water about 12%; NM2P about 3%; and triethylphosphate about 55%.

(3) Peroxide I about 30%; water about NMZP about 32% and triethylphosphate about 33%.

(4) Peroxide I about 30%; water about 30%; NMZP about 3% and propyleneglycol about 37%.

(5) Peroxide I about 30%; water about 12%; NMZP about 3% andtetrahydrofurfuryl alcohol about 55%.

All of these five formulations have an active oxygen content of close to4%.

It has been discovered that the mixture of peroxide I and unsaturatedpolyester resins alone or in combination with ethylenically unsaturatedco-reactant has an exceptionally long pot life-in the absence of metalactivator-as compared to a mixture of unsaturated polyester resin andMEK peroxide. Thus, the invention contemplates a curable resin admixtureconsisting essentially of peroxide I in a curing amount, and anunsaturated polyester resin preferably including an ethylenicallyunsaturated co-reactant such as a styrene or allyl phthalate.

More preferably the curing resin admixture consists essentially ofunsaturated polyester resin and a curing amount of a peroxideformulation consisting essentially of about 35% of peroxide I, not morethan about 35% of water, and about 1590% of the hereinbefore definedorganic liquid solvent. Commonly, this admixture will include anethylenically unsaturated co-reactant.

It is to be understood that when rapid moderate temperature cures aredesired a metal activator as hereinbefore defined will have to be addedto the above defined curable resin admixture.

The peroxide I curing agent and the hereinbefore defined formulationsmay be used with unsaturated polyester resins systems which include aninhibitor. Known inhibitors which include all the conventionalcommercial materials now in use have been tried with peroxide I andsuccessful cures have been obtained.

Inhibitors which have been tried are:

p-Benzoquinone, t-butyl catechol, 2,5-di-phenyl-p-benzoquinone,2,5-d-t-amyl hydroquinone, 2,5-di-t-butyl hydroquinone,toluhydroquinone, 2,5-di-t-butyl quinone, HPT (Eastman ChemicalProducts), p-octylphenyl salicylate, resorcinol mono benzoate,tecquinol, 2,4,5-trihydroxy butyrophenone, 2,5-diphenol quinone,monotertiary butyl hydroquinone, hydroquinone and toluquinone.

It has been observed that the amount of inhibitor present does haveinfluence on the curing time with peroxide I as the catalyst. However,it has been observed that rapid cures can be obtained even with presentsys tems heavily loaded with inhibitors by increasing the amount ofperoxide I added.

The curing effectiveness of peroxide I is demonstrated and compared tothe effectiveness of 'a commercially available MEK peroxide formulationand the commercially interesting characteristics of a large range offormulations of peroxide 1 are set forth in the following tests. It isto be' understood that these tests are not introduced to demonstrate allformulations or possible resin systems and, therefore, do not limit thescope of the invention herein described.

ILLUSTRATIONS AND COMPARISONS Tests A The flash point, ignition andburning characteristics, and ability of the formulation to be dilutedwith diallyl phthalate (DAP) was studied on a general formulation havinga 4% active oxygen content:

The ignition and burning times were determined on a 2 gram sample indirect contact with a Bunsen burner flame. The ability to accept DAP wasdetermined by adding the phthalate to the formulation until a secondphase appeared.

Methanol, ethanol and isopropanol gave the only formulations with aflash point below 200 F. With peroxide I, formulations with the flashpoint is determined by the solvent rather than by the peroxide as in MEKperoxide formulations.

Butylene glycol, ethylene glycol, propylene glycol,N-methyl-Z-pyrrolidone, pent-oxol, tetrahydrofurfuryl alcohol, Carbitol,Cellosolve, butyl Cellosolve and Cellosolve acetate formulations wereslow burning after long exposure to the flame.

Diacetone alcohol gave a formulation having 'a 35 second short ignitiontime.

The triethyl phosphate formulation did not burn.

CATALYTIC TEST PROCEDURES Catalytic activities were determined at 30 C.or room temperature (232S C.). Gel and cure times were measured with aSunshine gel-time meter, Model 22, exotherms recorded on aMinneapolis-Honeywell strip chart recorder, Model 14, with Type Ithermocouple.

So that the test work could be compared, studies were conducted in astandard polyester resin system having the composition shown in Table I.For practical evaluation, a number of commercial resins were used.

TABLE I.BASI-C POLYESTER RESIN SYSTEM Maleic anhydride, 1.0 mole n]Phthalic anhydride, 1.0 mole Propylene glycol, 2.2 moles }70%. Acid No.,45-50 Hydroquinone, 0.013%

The formulation of the inventionhereinafter called Form 'Iused in thecatalytic tests consisted of:

Styrene monomer Percent Peroxide I 30 Water 12 N-methyl-Z-pyrrolidone 29Triethyl phosphate 29 and had a 4% active oxygen content.

A commercial comparison formulation DDM consisted of methyl ethyl ketoneperoxides, water and dimethyl phthalate and had a 11% active oxygencontent.

Hereinafter the expressed catalyst amounts mean weight of formulationcontaining the particular peroxide, i.e. 1% of Form I actuallyrepresents 0.3% of peroxide 1.

Test B.Drift A characteristic of methyl ethyl ketone peroxide solutionis a drift in activity. This activity drift is evidenced by markedchanges in resin gel times. Table 2 shows 30 gel times measured over aperiod of eight weeks for 1% Form I plus 0.2% cobalt naphthenate (6%) inthe basic polyester resin system. No significant change was detected.

TABLE 3.CATALYTIC ACTIVITY DRIFT30 C. GEL TIIVIE Time in Minutes StorageTemp., C 4

Storage time:

Test C.-Variation of catalytic activity with catalyst concentrationTable 3 illustrates the wide range of activity that can be obtainedsimply by varying concentrations. Cures are obtained at 0.5% which areequally as good but somewhat slower than those concentrations at 1.0%.(To obtain even slower cures, the promoter lever should be decreased,rather than catalyst level.) Data in Table 4 show that the effect of atwenty-fold change in cobalt naphthenate concentration produces about aten-fold change in gel and cure time, at 1% catalyst addition.

TABLE 3.VARIATION OF CATALYTIC ACTIVITY WITH CATALYST CONCENTRATIONCatalyst Form I DDM Catalyst added, percent 1.0 0.75 0. 1.0 0 30 C. Gel(min.) 9. 8 15. 4 23. 3 30. 3 25 0. Gel (min) 18.0 28. 7 41. 7 47. 8 25C. Cure (min) 22.1 34.0 50. 7 82.1 Peak Exotherm F.) 320 318 294 183Barcol I 40-50 40-50 35-45 3040 TABLE 4.VARIATION OF ACTIVITY WITHCOBALT NAPHTHENATE ADDED Percent Cobalt Naphthenate (6%) 30 C. Gel (min)25 C. Gel (miu.). 26. 0 25 C. Cure (min.) 30. 5 Peak Exotherm, F .1 32308 Barcol I 45-50 40-50 40-50 2 The use of peroxide I in singlypromoted resins thus offers the advantage of a Wide range of activitypreviously possible only with the use of doubly accelerated resins,without the disadvantage of short resin shelf-life, as establishedbelow.

Test D.Variation of gel time with temperature The catalytic activitiesof MEK peroxides are temperature dependent. Table 5 shows how gel timevaries in the basic resin catalyzed by 1% Form I and 1% DDM, over thepractical Working temperature range; 16 C. to 30 C. (608 F. to 86.0 F.).

TABLE 5 Time in Minutes 1% Form I Temperature F.)

1.0% DDM Test E.Pot life In two component systems, in which one portionof the resin contains all the promoter and the other, all the peroxidecatalyst, it is necessary that the catalyzed portion of resin remainungelled for at least several days. In Table 6 are shown the pot livesof six commercial unpromoted resins catalyzed with 1% Form I compared tothose catalyzed with 1% DDM. The data show that several weeks shelf-lifeis possible with Form I, compared to a day or less with DDM.

TABLE 6 Gel Time (Days) Commercial Resin Form I DDM 1 1e 1 5 1- 15 1Test F The effect of varying the amount of inhibitor added was studiedusing 1% of Form I and 0.5% cobalt naphthenate (6%). The results areshown in Table 7. (It is pointed out that the effect of inhibitor can becounteracted by using more peroxide 1.)

TABLE 7.EFFECT OF INCREASING INHIBITOR ADDITION [25 C. cure data]Hydroquinone, Gel Time Cure Time Peak Exo- Barcol Percent Inhibitor(min) (men) therm, F. I

7 Test G In another study, polyester resin laminates were prepared f'romformulations of peroxide I at the 4.0 percent active oxygen level.Formulation II consisted of peroxide I, 30%; water, 12% andN-methyl-Z-pyrrolidone, 58%. Formulation II consisted of peroxide I, 30%water, 12%; and Cellosolve acetate, 58%. These were compared with DDMcontaining 11.0 percent active oxygen, at 1.0 percent catalyst addition.In the laminate tests, fiberglass cloth was impregnated with catalyzedpolyester resin, then the rate of hardening and curing at 24 C. wasobserved. After initial gelling took place, Barcol hardness measurementswere taken at minute intervals for 60 minutes and again after standingovernight. Other samples were tested after storage for 1 hour at 100 C.The results of these tests are set out in Table 8.

The gel time is the point at which the sample first solidifies. Thefirst Barcol reading is taken at the point at which the laminate becomesfirm. At this point the laminate usually is no longer sticky and can behandled carefully. At a reading of about Barcol 30, the laminate is hardenough to handle and can be transported or stacked in piles. This issignificant to the fabricator in that it determines when his molds canbe released for another operation.

It is seen in Table 8 that laminates catalyzed with peroxide I gelled inabout 25 minutes and were firm enough for a Barcol reading after about38 minutes. DDM had a slower gel time and required about 3 times as longfor a Barcol reading.

The laminates prepared from peroxide I gelled and hardened much morerapidly than those prepared from DDM. Thus, in a total time of about 40minutes after preparation began, the laminate from peroxide I could behandled. They could then be removed in about 50 minutes, with the entireoperation requiring less than an hour. With the DDM there was timeperiod of more than an hour and a half before the laminate could behandled. Over 2 hours had passed before the molds were freed. Further,standing overnight or exposure to elevated temperatures were requiredfor the laminate to reach its final desired level of hardness. Thus,peroxide I saves about half the fabrication time and eliminates the needfor elevated temperatures.

ADDITIONAL DESCRIPTION AND TESTS The classes of preferred organic liquidsolvents which have substantial solubility in water are described inmore detail as:

(1) Lower alkanols. These have 14 carbon atoms. Illustrative aremethanol, ethanol, isopropanol, n-butyl alcohol and t-butyl alcohol.

(2) Benzyl alcohol.

(3) Lower glycols. These have 2-8 carbon atoms. Illustrative areethylene glycol; propylene glycol; 1,4- butanediol; 2-butene-1,4-diol;hexanediol and octanediol.

(4) Ether glycols. All the ether glycols are very water soluble and aresuitable for use as solvents in this invention. Illustrative arediethylene glycol, dipropylene glycol, tetraethylene glycol, and thepolyglycols in general. Higher molecular weight polyethylene glycols areavailable under the trademark designation Carbowax, e.g. Carbowax200-200 M.W.

(S Saturated heterocyclic diethers having only carbon, hydrogen andoxygen atoms and 3-4 carbon atoms in the ring. Illustrative are dioxaneand dioxolane.

(6) Alkyl and cycloalkyl ketones having a total of 3-7 carbon atoms.Illustrative are acetone; methyl ethyl ketone; ethyl isopropyl ketone;mesityl oxide (4-methyl-3- pentene2-one); isopropyl butyl ketone;butanedione; pentanedione-2,4; hexanedione; cyclobutanone,cyclohexanone, methylcyclohexanone and dime=thylcyclobutanedione.

(7) Lower alkyl esters of lower alkanols, lower glycols and etherglycols. Lower alkyl has 16 carbon atoms. Illustrative are methylacetate, ethyl acetate, methyl propionate, ethyl butyra-te, ethyleneglycol mono'acetate, ethylene glycol diacetate, hexanediol dipropionate,butanediol dihexanoate, and Carbowax 200 diacetate.

(8) Saturated monohydric ether alcohols having a total of 4-8 carbonatoms. Illustrative are tetrahydrofurfuryl alcohol and Pentoxol(4-methoxy-4-methyl pentanol-Z).

(9) Ketoalkanols and lower alkyl esters of ketoalkanols. These have 48carbon atoms in the ketoalkanol portion. Illustrative are diacetonealcohol; 4-hyd'roxy-2- butanone; ethyl acetoacetate and methyllevulinate.

(10) Lower alkyl esters of phosphoric acid. Illustrative are dimethylphosphate, triethyl phosphate and tributyl phosphate.

(11) N-R-Z-pyrrolidone where R is alkyl having 14 carbon atoms.Illustrative is N-methyl-Z-pyrrolidone.

(l2) R-ethers of lower glyclos and ether glycols where R is lower alkylor phenyl.

(l3) Mono-R'-ether, mono-lower alkyl ester of lower glycols and etherglycols where R is lower alkyl or phenyl.

Illustrative of 12 and 13 are the surfactant Tergitol NPX (nonyl phenylpolyethylene glycol ether), and the compounds sold under the trademarkdesignation Cellosolve and Carbitol. Typical of these are: butylCellosolve (ethylene glycol monobutyl ether); 'butyl Cellosolve acetate(ethylene glycol monobutyl ether aceate); Cellosolve acetate (ethyleneglycol monoethyl ether acetate); Cellosolve (ethylene glycol monoethylether); dibutyl Cellosolve (ethylene glycol dibutyl ether); nhexylCellosolve (ethylene glycol monohexyl ether); methyl Cellosolve(ethylene glycol monomethyl ether); methyl Cellosolve acetate (ethyleneglycol monomethyl ether acetate); phenyl Cel'losolve (ethylene glycolmonophenyl ether; butyl Carbitol (diethylene glycol monobutyl ether);butyl Carbitol acetate (diethylene glycol monobutyl ether acetate);Carbitol acetate (diethylene glycol monoethyl ether acetate); Carbitol(diethylene glycol monoethyl ether); dibutyl Carbitol (diethylene glycoldibutyl ether); diethyl Carbitol (diethylene glycol diethyl ether);n-hexyl Carbitol (diethylene glycol monohexyl ether); methyl Carbitol(diethylene glycol monomet'hyl ether).

(14) Di-R"alkali metal sulfosuccinate where R" is alkyl and has 6-16carbon atoms. These compounds are surfactants and are illustrated byMonowet MT (ditridecyl sodium sulfosuccinate).

Test H For comparison purposes pure3,5-dimethy1-3,5-dihydroxy-l,Z-peroxycyclopentane (Peroxide I), a watersolution of Peroxide I, and numerous solutions of different solventswere tested for effectiveness as polyester resin curing catalyst. Thetest procedures were the same as those set out supra under CatalyticTest Procedures and the resin was the same as described under Table I,supra. The tests were carried out with 0.2% cobalt naphthenate (6%)added 'to the resin.

Each of th Peroxide I solutions was adjusted to have an active oxygencontent of 4% and 1% of solution by weight was used as catalyst.

TABLE 9 Time in minutes Peak Barcol Test Solvent 30 0. Room RoomExotherm, Hard- Gel Temp. Temp. ness Gel Cure 1 None 64.8 2 Water 17. 228. 4 42. 2 252 15-25 3... Isopropanol 9. 3 16. 4 21.4 304 40-50 4Benzyl Alc0hol.-.. 8. 5 16. 5 20. 6 308 40-50 5 Propylene glycol. 8. 015. 5 19. 0 314 40-50 6 2-butene-1,4-diol.... 7. 5 13. 5 17. 0 308 40-507 Dipropylene glycoL. 11.4 19.8 25.2 300 40-50 8 Carbowax 200 8. 4 16. 220. 5 301 40-50 9 Dioxane 9. 8 17. 6 22. 1 298 40-50 10.. Methyl ethylKetone. 7. 4 14. 7 18.6 300 40-50 11.. lVIesityl Oxide.. 6. 5 12. 8 16.5313 40-50 12.. Acetyl Acetone. 5.0 11.0 14. 5 316 40-50 13.- Ethyleneglycol diacetate 9. 6 17. 1 22.0 302 40-50 14.. TetrahydrofurturylAlcohol. 7. 3 13. 9 18. 1 312 40-50 15.. Pentoxol 8. 6 16. 4 21.0 30340-50 16.. Diacetone Alcohol..... 7. 1 14. 7 19. 1 310 40-50 17..4-hydroxy-2-butanone- 7. 1 13. 5 18.2 308 40-50 18.. Ethyl acetoacetate-6. 4 12.1 17.0 296 40-50 19.. Methyl levuliuate... 7. 2 13. 5 17 4 29440-50 0 Triethyl Phosphate 9. 5 16. 2 21.5 290 40-50 21 N-methyl-2-pyrrolidone 8. 6 14. 7 19. 6 300 40-50 22 Cellosolve 9. 4 15.8 20. 5 299 40-50 23.- Methyl Cellosolve acetate 8. 9 15. 8 20. 6 30240-50 24 Diethyl Carbitol 7. 6 13. 8 18.2 317 40-50 5 Dibutyl CarbitoL.9. 3 16. 9 21.9 301 40-50 26.. Carbitol Acetate. 8. 4 15.7 19.9 30340-50 27.. Tergitol NPX... 7.8 14.7 19.1 303 40-50 28.. Monowet MT70 7.4 13. 7 17. 7 308 40-50 The results of these tests are set out in Table9. The pure Peroxide I is very slightly soluble in the resin and thelong gel time (Test 1) at 30 C. (86 F.) is believed to be caused in partby the difficulty in getting an intimate dispersion of the .solidperoxide into the resin. The water solution of Test 2 shows improvementover Test 1 but is still poor in terms of times and very poor in theimportant Barcol Hardness. All of the solvents of the invention gaveoutstanding room temperature results, especially in the Barcol hardness;the variations between solvents is not commercially significant.

All of the solvents in Table 9 have at least substantial solubility inwater. Inspection of the table establishes that regardless of thechemical class of solvent, all afford equivalent results when usedaccording to these conditions. The requirements of being a liquid andsubstantial solubility in water distinguish each class as demonstratedby the species given in Tables 9 and 10.

Test J TABLE Formulation A B C Time in Minutes:

. G 7. 7 7.0 9. 4 R T. Gel..- 13. 7 12. 0 16.3 R.'I. Cure 17.2 15.8 20.6Peak Exotherm, F. 317 312 302 Barcol Hardness 40-50 40-50 40-50 Thepresence of the large amount of water surprisingly did not adverselyaffect the curing ability of the peroxide. The results are indeedsomewhat better than those shown in Table 9 for these solvents. Theability of the solvent to bring the water into solution in the resin isan important attribute to the commercial user.

Thus having described the invention, what is claimed 1s:

1. A method of curing an unsaturated polyester resin which methodcomprises:

(a) admixing said resin with a curing amount of 3,5-

dimethyl 3,5 dihydroxy 1,2-peroxycyclopentane, said peroxycyclopentanebeing admixed in the form of a solution formulation consistingessentially of (I) said peroxycyclopentane and (II) organic liquidsolvent having substantial solubility in water, which solvent isselected from the class consisting of (1) lower alkanols;

(2) benzyl alcohol;

(3) lower glycols;

(4) ether glycols;

(5) saturated heterocyclic diethers having only carbon, hydrogen andoxygen atoms and 3-4 carbon atoms in the ring;

(6) alkyl and cycloalkyl ketones having a total of 3-7 carbon atoms;

(7) lower alkyl esters of lower alkanols, lower glycols, and etherglycols;

(8) saturated monohydric ether alcohols having a total of 4-8 carbonatoms;

(9) ketoalkanols and lower alkyl esters of ketoalkanols having 4-8carbon atoms in the ketoalkanol portion;

(10) lower alkyl esters of phosphoric acid;

(11) N-alkyl-2-pyrrolidone where alkyl has 1-4 carbon atoms;

(12) R'-ethers of lower glycols and ether glycols where R is lower alkylor phenyl;

(13) mono-R ether, mono-lower alkyl ester of lower glycols and etherglycols where R is lower alkyl or phenyl; and

(14) di-R"-alkali metal sulfosuccinate where R" is alkyl having 6-16carbon atoms; and

(b) maintaining said admixture at a curing temperature for a curingtime.

2. The method of claim 1 wherein said admixture includes anethylenically unsaturated co-reactant.

3. The method of claim 1 wherein said admixture includes a metalactivator for said peroxycyclopentane.

4. The method of claim 1 wherein the solution proportions are: (I) about10-50%; (11) about 15-90% and (III) water, not more than about 35%.

5. The method of claim 4 where the water content is not more than about15%.

6. The method of claim 4 where said peroxycyclopentane content is about20-40%.

7. The method of claim 1 wherein said organic liquid is propyleneglycol.

8. The method of claim 1 wherein said is hexylene glycol.

9. The method of claim 4 wherein said solution consists of about equalproportions of said peroxycyclopentane; water and hcxylene glycol.

10. The method of claim 2 wherein said co-reactant is a styrene.

11. The method of claim 2 wherein said co-reactant is an allylphthalate.

12. The method of claim 3 wherein said metal activator is a cobaltcompound.

13. The method of claim 12 wherein said curing temperature is about60-100 F.

14. The method of claim 1 wherein said formulation has an active oxygencontent of about l-6%. V

15. The method of claim 1 wherein said organic liquid constituentincludes at least about 3%, based on formulation, ofN-alkyl-Z-pyrrolidone where the alkyl group has 14 carbon atoms.

organic liquid 1 2 References Cited UNITED STATES PATENTS 3,149,1269/1964 Milas 260-338 3,151,170 9/1964 Davis et al. 260-861 3,222,29412/1965 Meyer 260-861 3,333,021 7/1967 Geipert 260-863 FOREIGN PATENTS1,128,135 4/1962 Germany.

1,164,086 2/ 1964- Germany.

OTHER REFERENCES Mageli et al., Correlation of Peroxide Half-Life withPolymerization, Modern Plastics, March 1959, pp. 135- 137, 140, 144 and172, Class 260-861.

' SAMUEL H. BLECH, Primary Examiner.

M. TILLMA-N, Examiner.

20 J. T. GOOLKASIAN, Assistant Examiner.

